In a gas turbine engine, air is pressurized in a compressor and mixed with fuel in a combustor and ignited for generating hot combustion gasses which flow downstream through several turbine stages. A turbine stage includes stationary turbine vanes extending radially between inner and outer castings. The vanes are hollow with openings that mate to openings within the castings. The vanes have airfoil configurations for guiding the combustion gasses between corresponding turbine rotor blades disposed downstream of the vanes. The blades are mounted to the perimeter of a rotor disk that rotates during operation for providing power to turn the compressor or fan during operation.
Since the turbine vanes are heated during operation by the hot combustion gasses which flow thereover, cooling air bled from the compressor is channeled inside the vanes for cooling thereof. Typically, the cooling air flows toward the center of the turbine as the air passes through the vanes. In order to channel the cooling air through the vanes, the outer casing is fitted with a cover to create a plenum. The cover encases the compressed cooling air openings that mate with the vane openings. The cover has an opening to accommodate a spoolie boss which allows air to enter the plenum.
During normal operations, the cover may collapse due to engine cycling. This collapse is associated with cover distortion and elongation as well as spoolie boss distortion. While it is not known exactly why the plenum covers become distorted, it is believed that an adverse thermal gradient is responsible, with pressure changes possibly also an associated factor.
In order to repair the cover, a typical procedure involves removing the cover, installing a repair cover, and then attaching a spoolie boss to the cover. Additionally, if a borescope hole is desired, existing methods require machining the repair cover after installation. This method requires multiple repair steps which increase repair costs. What is needed is a method of repairing a plenum cover that requires fewer steps, lowers repair costs, and produces a repaired part that meets or exceeds OEM performance specifications.